At present, a conventional ceramic bowl is obtained by pressure-casting a suspension referred to in the technical jargon of the sector as “slip”.
The bowl is composed of two parts which are combined with each other: a first operative bottom part, or “active part”, comprising a pan and a drainage siphon (namely the inner zones of the bowl), and a second top part or “rim”.
In this connection, the first part or active part constitutes the functional part of the bowl and must have dimensional characteristics which are suitable for ensuring correct operation of the bowl as a pan for collecting and discharging the liquid flow.
The rim has a portion thereof configured to reproduce the extension of the top edge of the pan which it covers (for example, but not necessarily, an ellipsoidal form) and a rear extended part which is parallel to the extension of the siphon and in which a through-hole for supplying the flushing water is formed.
This rim part may be made in two definite forms which are referred to in the technical jargon of the sector as “open rim” and “closed rim”.
In the case of an open rim its portion covering the edge of the pan has a cross-section in the form of an overturned “U” with its bottom surface open so as to allow the passage of the flushing water.
In the case of a closed rim, instead, its portion covering the edge of the pan has a cross-section of the partially closed toroidal type in which, on the wall facing the pan, a plurality of convolutions or holes for discharging the water are formed.
In this connection, in the manufacturing technology based on the high-pressure casting of slip inside moulds, the active part and the rim are made separately (at least as regards the said closed rim).
Only subsequently are the rim and the active unit joined together by bonding the rim onto the top edge of the pan.
The joining operation is performed using the parts in a “fresh” state, i.e. when the parts still have a high percentage of water and have just been extracted from the mould. The reason why the parts are bonded in the fresh state is that, following bonding, the parts may undergo finishing (performed also using robot units), ensuring a good surface continuity, i.e. an attractive appearance of the bowl.
In the current market there is an ever-increasing demand for toilet bowl designs which are such that large areas of the functional components (viz. pan) must be covered and that essentially casings of different shapes and sizes must be provided in each case.
In order to be able to produce this type of bowl it is required to create moulds with very large and complex “free thickness” zones with consequent high costs and not insignificant problems from a technological point of view.
In fact, “free thickness” moulds allow maximum freedom as regards the aesthetic form of the articles, with different dimensional ratios inside the mould and, therefore, with the presence of large-volume casting cavities.
In this connection, the cavity inside the mould is not distinguished by a male/female mating arrangement (as in preset-thickness moulds), but the walls of the product are formed by a single internal surface of the mould.
Basically, therefore, the requirement for bowls with different aesthetic designs results in a reduction in standardization of the manufacturing parts with a corresponding diversification both of the mould types and the manufacturing operations with a possible increase in cost of the finished article.
An example of a bowl is known from the document US 2005/0166308 where the rim is bonded onto the pan after the corresponding forming operations inside two different moulds.
The pan is formed with outer covering walls formed simultaneously with its functional inner part, so as to act as an outer support structure which in practice is varied depending on the type of aesthetic model to be produced.
The Applicant, therefore, in an attempt to respond to this demand more effectively, has devised a ceramic toilet bowl described in patent application EP 2017391.
In this solution the bowl comprises a first bottom part, which is composed of the liquid collection pan with a liquid-drainage siphon portion, and a second top part or rim, which is composed of the front portion forming the top edge of the pan and a rear extended part inside a liquid passage channel is provided.
The bowl is formed with at least the pan and the rim (and optionally also the siphon) as a single body inside the mould so as to define a single part to which a third covering part, or outer casing, is added, the latter housing the single part configured so as to be joined to the casing at least along the top edges of the latter.
With such a design of toilet bowl it is possible to manufacture a single standardized part comprising all the functional components of the product, while the aesthetic features of the final product are provided on the casing portion.
However, during the industrial implementation of this solution, a number of problems associated with the particular configuration of the rim and the consequent structural design of the moulds required to produce the bowl have arisen.
In particular, the perimetral form of the rim and, secondarily, if present during casting in the mould, the configuration of the siphon, create particular undercuts or recesses and/or projections in the form of the product such as to require the presence of at least three mould parts in order to obtain the part: two lateral half-moulds, configured to obtain the outer surface of the finished part, and a central piston/mould for closing the first two half-moulds in order to produce the inner rim/pan part and, optionally, the siphon.
In addition it should be added that the mould may have up to four parts, for particular bowl designs, with the introduction of an insert which is separate from the lateral parts.
This mould is therefore managed, when opened and closed, by means of movements along a horizontal axis (first two lateral mould-halves) and along a vertical axis (central piston/mould).
In this connection, therefore, the plant required to produce the bowl in question requires essentially at least two moulds consisting of three parts, each of which with a corresponding movement necessary for: forming the pan/rim component (with optional siphon) as one piece and a similar mould for the production of the casing.
The large number of said components thus complicates, increases the cost and also partly slows down the production of the bowl thus designed, cancelling out partly the advantages resulting from the standardization of the product thus configured.